Field of the Invention
The present disclosure relates to a method for processing a silicon substrate and a method for manufacturing a liquid ejection head.
Description of the Related Art
In common processing of micro electro mechanical systems (MEMS) and processing of some semiconductor devices, there are many examples of processing of structures that penetrate silicon substrates or have depths almost equal to the depths of the silicon substrates. In order to protect the walls of the structures from coming into contact with chemical agents and the like during production and use and to electrically insulate the structures, some protective films may be formed and protective films for the bottom section may be removed for the purpose of enabling communication with devices disposed on the bottom surface side of the structures. Examples of such structures include a supply port of a liquid ejection head and a penetrating electrode of a penetrating wiring substrate. Hereafter a liquid ejection head will be mainly described below in detail as an example thereof.
At present, a silicon substrate used for the liquid ejection head is processed by applying a semiconductor device microfabrication technology. In a common liquid ejection head used for a liquid ejection printing system, a flow passage forming member is disposed on the silicon substrate.
The flow passage forming member forms an ejection port for ejecting liquid droplets and a liquid flow passage that communicates with the ejection port. In general, a plurality of liquid flow passages are arranged in a line. Ejection energy generation elements are disposed in a portion of the liquid flow passage on the silicon substrate, and liquid droplets are ejected from the ejection ports due to the energy generated by the ejection energy generation elements. The silicon substrate is provided with a plurality of supply ports that communicate with the respective liquid flow passages and a common liquid chamber that communicates with the supply ports.
In such a configuration, droplets are ejected from the ejection ports by, for example, heating and foaming a liquid by using thermal energy from the ejection energy generation elements, e.g., ejection heaters or the like. At that time, the liquid is supplied from the supply ports to the liquid flow passages and the liquid is supplied from the common liquid chamber to the supply ports.
Examples of methods for processing a silicon substrate used for such a liquid ejection head include a method involving two-stage etching of a silicon substrate, as described in U.S. Pat. No. 6,534,247. In this method, first etching is performed by employing crystal anisotropic etching so as to form a common liquid chamber. Then, second etching is performed by employing dry etching so as to form supply ports. According to this method, the silicon substrate is provided with the common liquid chamber and the supply ports that communicate with the common liquid chamber, and a structure penetrating the silicon substrate by combining the common liquid chamber and the supply ports is formed.
In general, silicon is etched by an alkaline solution. In the case where an alkaline liquid is ejected, the inner wall of the structure is dissolved, and the dimension of an opening may be changed. In particular, the wall of each of the supply ports described in U.S. Pat. No. 6,534,247 has low alkali resistance compared with the wall of the common liquid chamber formed by crystal anisotropic etching and, therefore, the above-described problem becomes significant. Consequently, a film (hereafter referred to as a protective film) is formed for protecting the wall, at which silicon is exposed, from an alkaline solution.
In many cases, the protective film is formed from the opening side of the structure of the liquid ejection head. The protective film is formed on the upper surface of the silicon substrate and the side wall of the structure. A flow passage forming member for demarcating the liquid flow passage and ejection ports may be formed on a second surface opposite to a first surface, on which the common liquid chamber and the supply ports are formed, of the silicon substrate. In that case, an etching stop layer or the like is disposed on the second surface of the silicon substrate such that the flow passage forming member is not affected during dry etching of the supply ports. Therefore, the protective film is also disposed on the bottom surface of the structure. However, it is necessary that only the protective film disposed on the bottom surface of the supply port be removed for the purpose of enabling communication with the ejection port side.
In general, dry etching is used for removing the protective film on the bottom surface. This is because the protective film on a horizontal surface is selectively removed and the protective film on a perpendicular surface is retained by introducing ions having directional properties.
Nowadays the same technique is also used for a through silicon via (TSV) which is discussed in a semiconductor production process. TSV is used to establish a connection with a wiring line on a back surface by forming a through hole in a silicon substrate provided with a semiconductor element. A protective film composed of an insulator is formed on a side surface of the TSV so as to electrically insulate the silicon substrate from the TSV. In this case as well, another device is present on the bottom surface of the through hole, a protective film is formed on the bottom surface of the through hole and, therefore, the protective film has to be removed.